engleski

Thermal performance analysis of fin-and-tube heat exchangers operating with airflow nonuniformity

This study develops a tube element method for thermal performance analysis of fin-and-tube heat exchangers operating with airflow nonuniformity. Experimental investigations have been performed on two fin-and-tube heat exchangers to validate the proposed tube element method. The heat exchanger tubes are discretized into a finite number of tube elements. These tube elements are observed as distinctive sub-exchangers, described by the appropriate heat transfer relations. The tube element method is capable of predicting the effectiveness in heat exchangers with complex tube circuitries, operating with either uniform or nonuniform airflows. The following general conclusions are obtained: the size of the effectiveness deterioration depends mainly on the heat exchanger operating point and on the degree of airflow nonuniformity. The effectiveness deterioration is highest when the heat capacity rate ratio is 1 and lowest when the heat capacity rate ratio is 0, for airflow nonuniformities with orientation perpendicular to the tube axis. The opposite is seen for airflow nonuniformities with orientation parallel to the tube axis. The heat exchanger effectiveness deterioration is up to 5.2% and 14.5% for complex nonuniform airflow profiles encountered in real-world operation, having airflow nonuniformity degrees of 0.43 and 0.81, respectively. Further, it was found that the heat exchanger tube circuitry design, the thermal resistance ratio and the airflow regime also influence the size of the effectiveness deterioration.

Airflow nonuniformity ; Fin-and-tube heat exchanger ; Effectiveness deterioration ; Thermal performance ; Experimental validation

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